1. Field of the Invention
The present invention generally relates to a semiconductor device and a method of producing the semiconductor device. More particularly, the present invention relates to a semiconductor device having a heat spreading plate for spreading heat generated in the semiconductor chip during operation.
Due to a high-density structure and increased power consumption, recent semiconductor chips tend to generate an increased amount of heat. Accordingly, the semiconductor device having a semiconductor chip thereon may be provided with a heat spreading plate for efficiently dissipating heat generated in the semiconductor chip.
In use, the semiconductor devices may be mounted on various electronic apparatuses requiring high reliability. Accordingly, a high reliability is required for the semiconductor devices.
2. Description of the Related Art
FIG. 1 illustrates a conventional fine-pitch type semiconductor device 1. This semiconductor device 1 has a package structure called FBGA (Fine-pitch Ball Grid Array). The semiconductor device 1 includes a semiconductor chip 2, a wiring board 3, solder balls 7, and a sealing resin 8.
The semiconductor chip 2 has a high density, and is fixed with an adhesive 5 onto the upper surface of the wiring board 3, which functions as an interposer. The wiring board 3 is a printed wiring board or a flexible printed board (in FIG. 1, a flexible printed board is shown). The wiring board 3 has a polyimide tape and a wiring layer 4 formed thereon. The wiring layer 4 and the semiconductor chip 2 are electrically connected by wires 6.
Openings are formed at predetermined positions of the polyimide tape, and the solder balls 7 are attached to the wiring layer 4 through the openings. Thus, the semiconductor chip 2 is electrically connected to the solder balls 7, serving as external connection terminals, via the wires 6 and the wiring layer 4.
The sealing resin 8 is molded to cover the semiconductor chip mounting surface of the wiring board 3, so as to protect the semiconductor chip 2, the wiring layer 4, and the wire 6.
As has been described above, due to a high-density structure, and increased power consumption, recent semiconductor chips tend to generate an increased amount of heat. However for the semiconductor device 1 shown in FIG. 1, the only heat transfer path for the heat generated in the semiconductor chip 2 is through the sealing resin 8 or the wiring board 3. However, the resin material used for the sealing resin 8 and the wiring board 3 is not particularly efficient with respect to the heat transfer characteristic.
Thus, the heat spreading efficiency of the semiconductor device 1 of the related art will be low, resulting in an insufficient spreading of the heat generated in the semiconductor chip. As a result, the semiconductor chip 2 is overheated, and may cause a faulty operation of the semiconductor device 1.
In order to overcome such over-heating problem, a semiconductor device having a heat spreading plate thermally connected to a semiconductor chip is known from Japanese Laid-Open Patent Application No. 7-283336. The known semiconductor device is provided with a heat spreading plate which is attached to a wiring board by an adhesive. Also, the semiconductor chip is directly mounted on the heat spreading plate which is exposed at an upper surface of the semiconductor device. The heat generated in the semiconductor chip is transferred to the heat spreading plate by direct thermal conduction and is radiated from the heat spreading plate. Thus, an efficient cooling of the semiconductor chip is achieved with the known semiconductor device.
However, with the semiconductor device having a heat spreading plate attached to the wiring board using an adhesive, the heat spreading plate may peel off from the wiring board due to aging of the adhesive. Thus, the use of an adhesive results in a drawback that the reliability of the semiconductor device is reduced.
Also, a method of producing the known semiconductor device requires a step of applying the adhesive to the heat spreading plate or to the wiring board. Since it is difficult to automate the adhesive-applying step, there is a drawback that the cost of producing the semiconductor device is increased.
Accordingly, it is a general object of the present invention to provide a semiconductor device and a method of producing the semiconductor device, which can overcome the drawbacks described above.
It is another and more specific object of the present invention to provide a semiconductor device having increased reliability.
In order to achieve the above objects according to the present invention, a semiconductor device includes:
a semiconductor chip;
a substrate electrically connected to the semiconductor chip and provided with external connection terminals on a first surface, the substrate electrically connecting the semiconductor chip and the external connection terminals; and
a heat spreading plate thermally connected to the semiconductor chip,
wherein the substrate is provided with joining parts made of metal on a second surface, the heat spreading plate and the substrate being joined together by welding the joining parts and the heat spreading plate.
The semiconductor device described above has an increased reliability, since the substrate and the heat spreading plate are joined without using the adhesive. There was a drawback with the semiconductor device using the adhesive in that the substrate and the heat spreading plate may peel off due to aging of the adhesive. However, with the semiconductor device of the present invention in which the substrate and the heat spreading plate are directly welded together, an aging problem can be reduced. Therefore, the substrate and the heat spreading plate are prevented from being peeled off and the reliability of the semiconductor device can be improved.
Also, since the semiconductor chip is attached to the heat spreading plate in a thermally connected manner, heat generated at the semiconductor chip can be efficiently spread and radiated. Thus, the semiconductor chip can be cooled in an efficient manner and false operation of the semiconductor device can be prevented.
It is still another object of the present invention to provide a method of producing a semiconductor device with reduced cost.
In order to achieve the above objects according to the present invention, a method of producing a semiconductor device includes the steps of:
a) forming a substrate provided with an opening formed at a substantially central position, interconnections and joining parts, one end of the interconnection being provided with an external connection terminal and the other end of the interconnection being electrically connected to a semiconductor chip;
b) forming a heat spreading plate having a fixed portion fixed to the substrate, a stage portion caved with respect to the fixed potion and connecting portions connecting the fixed portion and the stage portion;
c) fixing the heat spreading plate by positioning the stage portion at a position opposing the opening and then welding the heat spreading plate to the wiring board;
d) mounting the semiconductor chip on the stage portion through the opening;
e) electrically connecting the semiconductor chip and interconnections formed on the substrate; and
f) forming sealing resin on both sides of the heat spreading plate such that at least the semiconductor chip is sealed.
With the method described above, in the heat spreading plate fixing step, the heat spreading plate is welded to the substrate. Whereas in the prior art, the heat spreading plate and the substrate are fixed by the adhesive, so that a troublesome adhesive applying step was required. The adhesive applying step results in an increase in the production cost since it is difficult to automate.
The heat spreading plate can be welded to the substrate by, for example, laser welding method which may be easily automated. Also, it does not require troublesome step such as an adhesive applying step. Accordingly, it is possible to improve production efficiency and the process of fixing the heat spreading plate and the substrate can be implemented in a simple manner at low cost.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.